I don't think I've visited the homepage of https://www.google.com/ in a decade. The "I'm Feeling Lucky" button click rate probably dropped 99.99% ever since browsers started including search in the address bar.
Never. I use separate search and address fields for exactly this reason - to not reveal URLs to the search provider, and to not reveal searches to the DNS.
Yes, but the way that I have it configured, it is not confused with a search and a not search, so it does not have that problem. To search must be a colon and then specify what to be searched on and then a space and then the search query; if it does not start with a colon then it is treated as a relative (not absolute) URL.
I believe the about:config switches "browser.fixup.dns_first_for_single_words" set to false and "browser.urlbar.dnsResolveSingleWordsAfterSearch" set to 0 (zero) stop this.
Yeah Firefox leaks single words because it thinks it’s a localhost domain. You can avoid this by putting single words in “quotations”. Sad that you have to do that, but also: what’s your threat model?
I use the address bar for search all the time, not only bookmarks but also assigned search shortcuts.
That's why I always salt my one-word searches with a prepending random string.
Sometimes, but usually have a separate search field.